Re: [PATCH v4 2/7] iommu/core: split mapping to page sizes as supported by the hardware

[Joerg Roedel <Joerg.Roedel@amd.com>]

On Thu, Nov 10, 2011 at 01:12:00PM -0800, Stepan Moskovchenko wrote:
> I have been experimenting with an iommu_map_range call, which maps a
> given scatterlist of discontiguous physical pages into a contiguous
> virtual region at a given IOVA. This has some performance advantages
> over just calling iommu_map iteratively. First, it reduces the
> amount of table walking / calculation needed for mapping each page,
> given how you know that all the pages will be mapped into a single
> virtually-contiguous region (so in most cases, the first-level table
> calculation can be reused). Second, it allows one to defer the TLB
> (and sometimes cache) maintenance operations until the entire
> scatterlist has been mapped, rather than doing a TLB invalidate
> after mapping each page, as would have been the case if iommu_map
> were just being called from within a loop. Granted, just using
> iommu_map many times may be acceptable on the slow path, but I have
> seen significant performance gains when using this approach on the
> fast path.

Yes, from a performance point-of-view that makes sense, as an addition
to the existing iommu_map interface. Are the pages in the list allowed
to have different page-sizes?


	Joerg

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